Method and apparatus for regulating combustion



Oct. 25, 1932. G. w. S MITH 1,884,897

METHOD AND APPARATUS FOR REGULATING COMBUSTION Original Filed July 29, 1927 4 Shets-Sheet 1 A INVENTOR I Ha M Oct. 25, 1932. G. w. SMI I'H 1,884,897

METHOD AND APPARATUS FOR REGULATING COMBUSTION Original Filed July 29. 1927 4 Sheets-Sheet 2 INVENTOR G. W. SMITH Oct. 25, 1932.

METHOi) AND APPARATUS FOR REGULATI NG COMBUSTION Original Filed July 29, 1927 4 Sheets-Sheet 3 I IN'IENTOR 0a. 25, 1932. w. MITH 1,884,897

METHOD AND APPARATUS FOR REGULATING COMBUSTION Original Filed July 29, 1927 4 Sheets-Sheet 4 fig 6. 8

I INVENTOR M W. M81

mmmmmm Patented Oct. 25, 1 932 UNITED STATES PATENT OFFICE GEORGE W. SMITH, 0F PITTSBURGH, PENNSYILIVANIA, ASSIGNOR T0 JOHN M. HOTWOOD,

OF PITTSBURGH, PENNSYLVANIA ,METHOD AND APPARATUS FOR REGULATING COMBUSTION Original application filed July 29, 1927, Serial No. 209,289. Divided and this application filed April 8,

This application is a division of my co- 4 pending application, Serial No. 209,289, filed July 29, 1927, for an improvement In fluid analysis. Claims on the method of analyzing a fluid mixture and the apparatus for fluid analysis are retained in said application Serial No. 209,289. Claims on the method of and apparatus for regulating combustion of fuel in a furnace are presented in the present divisional application.

The present invention relates to a method and apparatus for regulating combustion of fuel in a furnace in accordance with the composition, particularly the carbon dioxide content, of the gaseous products of combustion. The carbon dioxide content ofthe combustion gases is quantitatively determined by a comparison of the lamellar and turbulent dioxide in the combustion gases may be thus measured and used, preferably automatically, as a basis of furnace control so as to maintain the proper ratio of fuel and air for the best combustion.

In making suchdeterminations,the relative difference in resistance. of fluids to lamellar and turbulent flow is utilized. When a fluid is passed through arestricted pas sage of small cross section relative to its length. such as a capillary tube, a porous plate or a bed of granular material, at not too great a pressure, the flow takes place along relatively smooth flow lines and without eddies and is of the so-called lamellar or capillary type flow. The pressure drop across the passage is approximately p'rop'orti onal to the volume of the fluid passed (rate of flow) and to its viscosity. The pressure drop is pra tically independent of the den sity of the fluid. On the other hand, when a fluid is passed through a restricted opening of a diameter relatively large, as compared with its length, such as an orifice in a thin plate, or even through a tube under sufficiently high pressure, the flow is broken up into eddies and is said to be of the turbulent type of flow. The pressure drop across the orifice or passage in which the turbulent flow takes place in approximately proportional to the Serial No. 353,515.

square of the volume of the fluid passed (the square of the rate of flow) and to its density. The pressure drop is practically independent of the viscosity of the fluid.

ture. Knowing the relative resistance to lamellar and turbulent flow of two fluids, measurements of the resistance ofiered by the lamellar andturbulent flow of a mixture conb taining them, furnish a means for determinmg their relative proportions in the mixture. For example, if a restricted passageway in which lamellar flow prevails, such as a capillary tube, and a passageway in which turbulent flow prevails, such asa thin plate orifice, be placed in series and the fluid passed through both, the temperature. being maintained uniform, the relative pressure drops across the capillary tube and the orifice furnishes a means'for determining the density and viscosity of-the fluid. If the relative pressure drops be determined, first, for one fluid passed through the device, and then for another fluid passed through it, the relative pressure drops furnish a means for-determining the relative-proportions in a mixture of the two fluids when passed through the device. 1

I will now consider in somewhat greater detail the conditions of lamellar and turbulent flow and how the determination of these two types of flow afiords a means for the quantitative determination of the percentages of the constituent fluids in a mixture.

If a fluid be passed through a tube under sufliciently small pressure, the flow willin all cases be lamellar and the volume of fluid per unit of time (rate of flow) will increase in approximate proportion to the pressure gl'adicntalong the tube. As the pressure gradient is increased and the rate of flow increases in consequence, a pressure will be reached at which the rate of flow is no longer proportional to the pressure. This pressure is called the transition pressure or critical pressure, The pressure-flow relationship at this point is not definite as the flow at portions of the tube may be lamellar flow,

while at other portions it may be turbulent flow. As the pressure is increased beyond the transition range, or critical pressure, the flow throughout the tube becomes turbulent in character, and with further increases in pressure, the rate of flow increases as the square root of the pressure gradient. By operating with suitable flow restrictions and suitable pressure gradients, the flow can be made definitely lamellar or turbulent. In a restriction whereflamellar flow prevails under a constant pressure difference across the restriction, the rate of flow will be inversely proportional to the viscosity of the fluid flowing. The higher the viscosity of the fluid, the less fluid will pass, per unit of time, under the same pressure difference. If turbulent flow prevails in a restriction under a constant pressure difl'erencc over the restriction, the rate of flow of the fluid will be inversely proportional to the density of the fluid, that is to say, a fluid having a higher density will flow more slowly through the restriction than a fluid having a lowerdensity, under the same pressure difference.

Under conditions of lamellar flow the density of the fluid passed is of little or no influence; under turbulent flow, the viscosity of the fluid passed is of little or no influence. Accordingly, if a passageway in which lamellar flow prevails, such as a capillary tube, and one in which turbulent flow pre' va-ils, such as an orifice, be placed in series, and a fluid passed through them in series, a flow will be established which will depend upon the dimensions of the passageways, upon the difference between the initial or entering and the final or discharge pressures, and upon the density and viscosity of the fluid which passes; The total pressure drop between the initial and final pressures may be divided into two pressure drops (1) across the capillary tube, and (2) across the orifice which, when added together, give the total pressure drop. The pressure drop across the capillary tube and the pressure drop across the orifice will, of course, depend upon the dimensions, the rate of flow, and. the density and viscosity of the fluid. The pressure drop across the capillary restriction will be proportional to the rate of flow established and the viscosity of the fluid. The pressure drop across the orifice restriction will be propor- ,tional to the square of the rate of flow established and to the density of the fluid.

5 then the initial andfinal pressures be main- 7 tained constant and if the density and the viscosity of the fluid do not vary, the interee-see? mediate pressure, that is, the pressure at the point between the capillary tube and the orifice, will remain constant.

If the initial and final pressures be maintained constant, but the viscosity or the density of the fluid or both vary, then the rate of flow and the intermediate pressure will vary.

If the density of the fluid passing remains constant and the viscosity decreases, then under the same pressure drop across the capillary tube, more fluid can pass. Since, however, the density of the fluid has not changed, a higher pressure drop will be required across the orifice to pass this greater quantity of fluid. The pressure at the point intermediate the capillary tube and the orition, less fluid can pass per unit of time, and

the rate of flow is decreased. The density remaining the same, a lesser pressure drop will be required across the turbulent flow' orifice to pass this .lesser rate of flow. Accordingly, the pressure intermediate therapillary tube and orifice will tend to decrease until the proportionate pressure drops across the two restrictions correspond to the altered viscosity.

If the viscosity remains the same and the density increases, then a greater pressure drop will be required to pass the same volume of fluid in a unit of time across the turbulent flow orifice restriction, or under the same pressure drop, a lesser rate of flow will be established. Since the viscosity has not altered, this lessened rate of flow through the capillary restriction will require a lesser pressure drop, and the pressure drop at the po nt intermediate the capillary and orifice will tend to increase.

will tend to decrease.

The effect of varying viscosities and densi- In a similar manner, 1f the viscosity remains the same and the denslty decreases, the intermediate pressure ties can occur separately or concurrently..

If, for example, under a given initial and final pressure across a capillary tube and a thin plate orifice in series, the viscosity of the fluid increases, while the density decreases, the intermediate pressure will tend to fall by reason both of the increased viscosity and decreased density. Conversely, if the viscosity decreases and the density increases, the intermediate pressure will rise.

Since the viscosity and density of fluids are in general independent properties, fluids and I fluid mixtures can be found in which increased density is accompanied by decreased viscosity, increased density by increased viscosity, decreased density by increased Viscosity, and decreased density by decreased viscosity. It will be apparent that if a capillary tube and an orifice be placed in series and maintained under a constant initial and constant final pressure, and if both the viscosity and the density of the fluid increases, then the pressure intermediate the restrictions will tend to rise because of the. increased density but will tend to fall because of the increased viscosity. The intermediate pressure, therefore, will rise or fall, depending upon whether the change in Viscosity or change in density has the preponderating effect.

Since under definite conditions, the viscosity and density of the fluid are characteristic properties of the fluid, if two fluids having different viscosities and/or differentdensities be passed through the same lamellar andturbulent flow restrictions in series, the intermediate pressure will in general be different for each ofthe two fluids. Mixtures of two such' fluids having intermediate viscosities and intermediate densities will, when passed through this arrangement; give pressures at the point intermediate the two restrictions which will'd-epend upon the relative proportions of each of the two fluids in the mixture. Therefore, if the same pressure "drop be maintained across the lamellar and turbulent flow restrictions in series,-the variations in the intermediate pressures occurring. with different fluids or mixtures of fluids may be utilized in determining their densities and viscosities, or the percentage of a fluid in mixture. q

Such variations in the intermediate pressures may be observed by suitably calibrated pressure devices or they maybe utilized by means of suitable pressure-responsive devices for automatic control. The gaseous products of combustion may be passed at a constant pressure through an arrangement of a lamellar flow restriction and a turbulent flow restriction in series, and the variat on in the intermediate pressure he used to'measure the percentage of carbon dioxide; or by suitable automatic pressure-responsive mechanism,

. the variations in intermediate pressure may be utilized to automatically control the'conditions of combustionso as to maintain the desired percentage of carbon dioxide in the Figures 4, 5 and 6 are detail diagrammatic views showing modifications in the arrangement of the flow restrictions, C

Figure 7 is a detail view of the preferred device for filtering, humidifying and temperature controlling the gases;

Figure 8 is a detail view showing a porous plug form of capillary flow restriction; and

Figure9 is a detail view showing an adjustable form of capillary flowrestriction.

Before describing the combustion controlling system as shown in Figure 1 in detail, I will first briefly describe the lamellar or capillary flow and the turbulent flow restrictions and their action upon a stream of gas passed through them.

Referring first to Figure 3; which shows the simpler form of flow device, reference numeral 1 indicates a capillary tube and refercnce numeral 2 indicates an orifice. The fluid, usually a gas, flows through the capillary tube 1, and the orifice 2 in series in-the direction indicated by the arrow in Figure 3. The gas is supplied at a constant superatmospheric initial pressure maintained in the supply tube 3. The gas is discharged into the atmosphere from the orifice 2, so that the final pressure is atmospheric. There is a chamber 4: intermediate the capillary tube 1 and the orifice 2. A' pressure gauge 50!. is connected to indicate the pressure in' the chamber 4. This pressure is that which I have above referred to as the intermediate pressure, being the pressureat the point intermediate the capillary'or lamellar restriction 1 and the turbulent or orifice restriction 2. 1

- If a gas, say for example, air, is suppliedat the inlet tube 3 at a constant pressure, a flow is established through the device and an intermediate pressure is established in the chamber 4, which can be measured by the pressure gauge 5a. If a gas havinga different density and/orviscosity is supplied at the sameconstant pressure in the inlettube 3, a different condition of flow is maintained, together with a different intermediate pressure at point 4, or if a mixture of gases hav- "ing different densities and/or viscosities is passed through the device, a change in the relative proportions of the gases in the mixture will cause the flow to be changed and the intermediate pressure at the point 4 to vary. As a specific example, assume that a flue gas, such as that resulting from the com bustion of fuel in the furnace, is supplied to the inlet tube 3 under a constant pressure, and assume for the sake of simplicity that the humidity and temperature of the gas as sup plied to the inlet tube 3 are also maintained constantly: Flue gases, in general, consist principally of nitrogen, carbon dioxide and;

oxygen, together with smaller amounts of 1 carbon monoxide, hydrogen, and sulphur dioxide, which are relatively small compared with the amount of carbon dioxide present. Of the gases generally present in significant amounts, oxygen and nitrogen have about the same viscosities and densities as air. The viscosity of air at '50? F. is .000181 (in C. G. S. units). Its density can be taken as 1. The viscosity of carbon dioxide at 60 F. is .000146, and its density is 1.53. It will be seen that the density of carbon dioxide is over one and one-half. times that of air, while its viscosity is but a little over three-fourths that of the viscosity of air,

If flue gas is passed through the capillary and turbulent flow restrictions land 2 and the amount of carbon dioxide in the flue gas increases, the density of the flue gas will increase and its viscosity will be lowered. Gonsequently, the pressure drop over the capillary restriction 1 will tend to decrease and the pressure drop over the orifice 2 will tend to increase, so that the intermediate pressure at the point 4 will increase. Similarly, it the proportion of carbon dioxide in the flue gas decreases, theintermediate pressure at the point 4 will decrease. If the other conditions are maintained the same, the pressure variation at the point 4, which may be measured by a suitable calibrated pressure gauge will give an indication of the percentage oi carbon dioxide in the flue gas.

. In order to get a better determination of the analysis of the gas by the pressure variations at the intermediate point 4, it is preferable to proportion the capillary and orifice restrictions so that the pressure drop over the capillary or lamellar flow restriction 1 is large in comparison with the pressure drop across the orifice or turbulent flow restriction 2. If this be done, the flow of the through the device will be controlled primarily by the capillary tube 1, which we may I term, for convenience, the dispensing restriction, so that the variations in the intermediate pressure at the point 4 will have a relatively small effect upon the volume of gases flowing through the device. The pressure which is measured at the point 4 is the pressure over the turbulent flow orifice 2, and the orifice 2 may, for convenience, be designoted as the measuring restriction. For example, if the pressure in the inlet tube 3 be maintained at about eighty inches of water superatmospheric pressure, the pressure drop across the capillary tube 1 may be seventy.

seven inches of water, and the pressure drop across the orifice 2 may be three inches of Water.

Assume that the flue gas is supplied to the inlet tube 3 at a pressure maintained constant at eighty inches of water above the atmospheric or final pressure into which the gas is discharged from the orifice 2. If the carbon dioxide in the flue gas increases, the viscosity ofthe gas is lowered and a greater volume or gas will tend to flow through the capillary gases wages? the orifice 2 small in porportion to the pressure drop across the capillarytube 1, the efl'ect of this reacting pressure can be made relatively small. Therefore, the volume of the gas passing through the device at a constant initial pressure may be made to'depend primarily upon its viscosity, and density changes will have a relatively. small effect upon the volume of gas suppliedby the dispensing restrictibn 1 to the measuring restriction 2.

In the case of flue gas containing carbon dioxide, an increase in, the carbon dioxide content will, by lowering the viscosity, cause an increase in the flow of gas through the device, and the increase in flow, combined with the increase in density due to the increased carbon dioxide, will cause an increase in the pressure'drop across the orifice 2, as measured by a pressure gauge from the intermediate point 4. As can be shown by calculation, a greater percentage change in the pressure at the point 4 for a given percentage change in the carbon dioxide of flue gas can be attained by making the drop over the capillary tube 1 large in comparison with the drop over the orifice 2, tharrwould be the case if the pressure drops over the capillary tube and orifice were approximately equal. Moreover, by making the principal part of the pressure drop occur over the dispensing restriction which supplies the gas to the measuring restriction, a smaller absolute pressure may be secured atthe intermediate point 4 and one whichis therefore easier to measure.

Variations in the temperature and humidity of the gas also afiect the density and viscosity, and consequently affect the ratio of the pressure drops over the Iameller and turbulent flow restrictions for a. constant initial pressure. Also accidental variations in the mltial pressure,such as might be caused by changes in the blowing device, will cause variations in the intermediate pressure at the point 4. Furthermore, the pressure at the point 4 is to be measured against some pressure as a standard, which is usually the atmosph'eric pressure or that upon the dis-, charge side of the orifice 2. The pressure gauge, therefore, has toassume an initial pressure, say about three inches of water in the illustrated case referred to above. and the changes in pressure due tothe changes in the carbon dioxide content of the gases will produce changes which are additive or subtractiv'e from the three inch pressure, but which are small in comparison therewith. For these reasons, it is preferred to balance the pressure at the intermediate point 4 in the device for analyzing the mixture of gases, against an intermediate pressure 111 a similar device through which a gas of a fixed compositlon is supplied. By balancing the initial pressures, a more sensitive gauge may be used, since the pressure gauge will only have to measure the differential pressure. Also, by placing the two devices close to each other and humidifying the two-gases at the same temperature, the effect of temperature changes and concomitant humidity changes will tend to neutralize themselves between the two devices, one supplied with the gaseous mixture to be analyzed, and the other with a gas of fixed composition. Such an arrangement is shown in Figure 2.

In Figure 2, reference numerals 1 and 2 indicate, respectively, a capillary tube and an orifice through which the gas to beanalyzed, such as flue gas, is passed in the direction indicated bythe arrow. A gas is supplied at a constant pressure through the inlet tube 3. A chamber 4 is situated between the capillary tube 1 and the orifice 2, and the chamber 4 is connected to one end of a pressure gauge 5.

Reference numerals 6 and '7 indicate, re-

spectively, a capillary tube and an orifice similar to the capillary tube and orifice 1 and 2, and through which a gas, such as air, is passed.- The air is supplied at a constant pressure by an inlet tube 8. A chamber 9 is situated intermediate the capillary tube 6 and orifice 7 and is connected to the other end of the pressure gauge 5, so that the pressure gauge 5 indicates the differential pressure between the chambers 4 and 9.

The flue gas and'air are supplied to the apparatus by blowers 10 and 11, respectively, driven by a common motor 12. The flue gas passes through a device 13 (hereinafter described in detail) in which the flue gas is bubbled through water to filter it, humidify it and bring it to the water temperature. The air is passed through a similar device 14 in which it is filtered, humidified and brought to the same temperature as the flue gas passing through the device 13. The air and gas are then passed to the respective capillary tubes 1 and 6 through the inlet tubes 3 and 8. A constant pressure device is connected by the branch pipes 15 and 16 to the inlet tubes 3 and 8, respectively,-so that'a constant pressure is maintained the same across the two sets of capillary and orifice restrictions-1 and 2 and 6 and 7. As shown in the drawings, the constant pressure device 17 consists of a tube 18 which dips into a bath of liquid, preferably mercury. The blowers 10 and 11 supply more gasthan is passed through the capillary tubes 1 and 6, the excess gas passing out through the constant pressure device,

- which, thereby serves to maintain a 'constant and equal pressure across each set of capillary and orifice restrictions.

The inlet tubes from the filtering humidifying and constant temperature devices 13 and 14 preferablylie in proximity and the two sets of capillary tubes and orifices 1 and 2 and 6 and 7 also lie in proximity, so that they are subject to the same temperature effects. The temperature effects can therefore be substantially eliminated if the water baths in the humidifying devices 13 and 14 are kept at the same temperature.

The dimensions of the restrictions 1 and 2 and 6 and 7 are preferably so proportioned that there is substantially the same pressure drop over the two capillary tubes 1 and 6 and over the two orifices 2 and 7 pressures in the chambers 4 and 9 above atmospheric pressure therefore tend to balance each other-out, and the pressure gauge 5 can be made more sensitive, since it can serve as a differential gauge to measure the pressure differences between the chambers 4 and 9.

The composition of the air will, of course,

remain substantially constant. If desired, air may be passed through the capillary tube 1 and orifice 2 from the blower 11 for calibration purposes and the pressures in the intermediate chambers 4 and 9 made equal for air passing through both sets of restrictions. Then, if flue gas be afterward passed through the capillary tube 1 while air is passed through the capillary tube 6, the differential pressure between the chambers 4 and 9 as indicated by the pressure gauge 5 will indicate the increase in pressure at the chamber 4, due to the carbon dioxide in the flue gas. Changes in the amounts, of carbon dioxide in the flue gas will be reflected in changescarbon dioxide will lncrease the ensity and lower the-viscosity. of the flue gas.

Having thus described the general principles of the flue gas analysis by my device, I will next describe its application to the automatic control of furnace combustion so as to maintain the desired carbon dioxide content of the flue gases. As is well recognized in the furnace combustion art, the proportion of carbondioxide in flue gas is an indication of the conditions of combustion. Too little carbon dioxide indicates too much excess air, and too much carbon dioxide indicates insuflicient air for the best combustion. The optimum carbon dioxide content of the flue gas depends upon the particular type of furnace and fuel and may vary from about 11 to 17% in stoker and powdered coal fired furnaces. For most eflicient conditions of combustion in any particular furnace, the carbon dioxide content should be maintained at the percentage determined by experience to behest for that particular type of furnace and fuel. The coal is burned in the usual combustion chamber 21. The powdered coal is supplied by a powdered coal machine 22, in which the coal is pulverized and is blown in a powdered condition by the blower 23 through the supply pipe 24 into the combustion chamber. The carrying air is commonly known in the powdered coal art as primary air." The coal is supplied to the powdered coal machine from a hopper 25. A valve 26 regulates the coal supply of the powdered coal machine. The secondary air for combustion of the coal is supplied through the air duct 2'? by a forced draft blower 28. The air supply is controlled by a damper 29 in the air duct 27. I

The hot gases of combustion from the combustion chamber 21 go through the passes of the boiler 30 and through the boiler breeching 31 to the stack 32. The outlet of the gases is controlled by the stack damper 33.

The combustion in the furnace may be primarily controlled by any of the well known methods of combustion control. As shown in the drawings, the combustion is primarily controlled by a master regulator 34, which is operatedin accordance with the steam pressure which is supplied to the master regulator through a pipe 35,tapped from the steam header 36. Any of the well known forms of steam regulator may be used. The form illustrated in the well known Hagan regulator of the general type shown is the Hopwood Patents Nos. 1,338,924 and 1,371,243, and the Pecbles Patents Nos. 1,339,000 and 1,492,604. The details of construction and operation of the master regulator are old in the art and do not need to be described in detail. The master regula tor .is of the compensated type which operates by' an incremental movement so that it assumes intermediate positions for steam pressures intermediate the maximum and minimum for which it is set. The master regulator has a power cylinder with a piston having upwardly and downwardly extending rods 37 and 38,. to which are secured the ends of chains or cords 39 and 40, respectively.

The cord 39 is connected to the damper 33, so that the furnace draft is controlled in ac- :ordance with the steam pressure, the draft being increased for a decrease in the steam pressure. As is well known in the furnace art, a decrease or an increase of the steam pressure indicates an increase or a decrease in the demand for steam or the load upon the boiler, and the combustion must therefore be respectively increased or decreased for the boiler to carry the load. While the master regulator is shown as being operated-by steam pressure, it may be operated by steam flow or by a combination of steam pressure and steam flow. as will be readily understood by any one skilled in the furnace control art.

The chain 40 is connected to the valve 26 which controls the fuel supply, so that a decrease in steam pressure will be accompanied by an increased supply of fuel.

The pressure in the combustion chamber 21 is regulated and is preferably kept coni having a bell 43 indicated in dotted lines. A

' power cylinder having a piston provided with v a downwardly extending rod 44 is actuated in accordance with the pressure of the gases in the combustion chamber and regulates the position of the damper 29. If the pressure in the combustion chamber 21 falls below the pressure for which the device is set, the damper 29 is opened to the desired amount to supply more air from the forced draft and restore the desired pressure. If the pressure in the combustion chamber rises, the damper 29 is adjusted toward its closed position to cut down the air and reduce the pressure to the desired point. The regulator 41 has an incremental or compensated movement, so that the damper 29 may assume any desired position.

The primary control of combustion, as described above, is modified by a secondary control in accordance with the carbon dioxide content of the flue gases. The secondary control device is indicated generally by reference numeral 45 in Figure 1, and is shown inmore detail in Figure 2. A bight of the stack dampercontrolling chain 39'is passed over pulleys and around a pulley 46 carried content of the flue gas, so as to, move the stack damper 33 toward its closed or toward "its open position, respectively. A decrease in the carbon dioxide content below the predetermined amount'f orwhich the device is set indicates that too much air is being drawn through the furnace, and the damper 33 should therefore be adjusted toward its closed position to cut down the proportion of the air relative to that of the fuel. It

will be noted that the control of the air and fuel is primarily regulated by the master reg ulator, and that the air is secondarily controlled by the carbon dioxide analyzing device so as to adjust the proportions of air and fuel. While the carbon'dioxide analyz-.

ing device is shown as modifying the air control so as to' regulate the relative proportions of air and fuel, it might equally well be applied to modify the fuel controlling device, which also would result in the control of the proportion of air and fuel.

It will also be noted that while the carbon dioxide analyzing device operates as a'secondary control through the primary controlling system, the carbon dioxide analyzing device and the primary controlling system may operate independently of each other. For example, if the steam pressure remains constant, but the proportion of carbon dioxide in the flue gas varies, the gas analyzing device will operate to vary the air but without affecting the fuel feed. On the other hand, if the carbon dioxide content remains constant, but the steam pressure varies, the primary control will serve alone to regulatethe fuel and air necessary (for the change in load upon the boiler. Therefore, while it is preferred to have the flue gas analyzing apparatus operate through the draft controlling dampers and the control means therefor which forms a part of the primary regulation, the control in. accordance with the flue gas analysis might be otherwise and independently applied to the furnace.

Flue or combustion gas is tapped off from the boiler breeching through a tube 49 to the blower 10. From the blower 10 it passes through the device 13, which filters the gas, humidifies it and brings it to a predetermined temperature. This device is shown in detail in Figure 7 of the drawings. It cons'sts of a closed chamber 50 containing a water bath 51. The gas is discharged through a submerged nozzle 52 against an impingement plate 53, which is likewise submerged and bathed in the water bath 51. The im pin'gement upon the plate 53 of the stream of gas serves efliciently to remove practically all of the suspended dust and smoke parti eles. Since the gas is exposed to the water in finely divided bubbles, it is humidified, being saturated with water vapor at the temperature of the water bath. The gas is also brought to the temperature of the water bath,

which may be maintained'substantially constant, by circulating water through the de-' v1ce.

The device 13 is described .and illustrated in its structural details on pages 66 and 67 of Public Health Bulletin No. 144 of J anuary, 1925, entitled'Comparative Tests of Instruments for Determining Atmospheric Dusts, published by the United States Government Printing Oflice at Washington,'

D. C., for the United States Public Health Service under the Treasury Department.

The flue gas after being thus filtered, hu-

midified and brought to a predetermined temperature, passes to the supply pipe 3 and through the, capillary tube 1 and orifice 2 to the atmosphere. As before described, the intermediate pressure inthe-chamber 4 will vary with the percentage of carbon dioxide in the flue gas, and such variations may be used for automatically controlling the combustion to maintain the carbon dioxide content at the desired percentage. v

The intermediate pressure in the chamber 4 is balanced against the intermediate pressure in the chamber 9 between the capillary tube 6 and orifice 7 which is supplied with air. The air is supplied by a blower 11, driven from the same motor as the shaft 12, so that any change in the motor speed will equally affect the blowers 10 and 11 operating on the flue gas and air respectively. The air passes through a device 14, which is a duplicate of the device 13 and is illustrated in Figure 7, and in which the air is washed, humidified and brought to the'desired temperature. By maintaining the water baths in the devices 13 and 14 at the same temperature, the flue gas and air may be maintained at the same temperature as supplied to the gas analyzing restriction. As above described, a constant pressure device 17 serves to maintain a predetermined and constant pressure on both the air and the gas supplied to the inlet tubes 8 and 3.

Pipe connections 54 and 55 lead from the chambers 4 and 9, respectively, to two inverted bells 56 and 57. The pressure gauge 5 is tapped off from these pipe connections 54 and 55 and gives a visual indication of the differential pressure between the chambers 4 and 9. The bells 56 and 57 will be subjected to this differential pressure. The bells 56 and 57 are partially immersed in a water bath 58 in the chamber 59. The bells are carried upon opposite ends of a balance beam or lever 6.0, pivoted at 61. The two sets of flow restrictions may be calibrated for air flowing through them both, so that the pressures in the intermediate chambers 4 and 9 will'both be equal for air. For purposesof calibration, the blower. 10 may be supplied with air through abranch supply pipe 62, controlled by a valve 63. If the flue gas is shut off by a valve 64 and the valve 63 is opened, air may be supplied to the blower 10, and by closing the valve 63 and opening the valve 64, flue gasmay be supplied, as desired.

If the flow restrictions 1 and 2 and 6- and 7 are roportioned to give the, same pressures in t e chambers 4 and 9 for air flowing through both sets of flow restrictions, then when flue gas is passed through the flow restrictions 1 and 2, the pressure in the chamber 4 will be greater than that in the chamber 9 in proportion to the amount of carbon dioxide in the flue gas. greater pressure will therefore be applied to the interior of the bell 56 than to that ofthe bell 57, and the beam 60 will tend .to be tilted in a clockwise direct-ion as viewed in Figures 1 and 2. Anadjustable weight 65 is carried by the balance beam 60 and may be adjusted to hold the beam 60 in a horizontal or equilibrium position for a particular increased pressure in the bell 56 corresponding to the desired carbon dioxide content of the flue gas. If the carbon dioxide content increases above that to which the weight is set, the liquid will be displaced downwardly in the bell 56 and the bell will tend to rise, or vice versa, if the carbon dioxide content of the flue gas decreases. The movement of the balance beam 60, which is controlled by the carbon dioxide content of the flue gas, is transmitted through a rod 66 to actuate a pilot-valve 67, which controls the power cylinder 48. As the piston of the cylinder rises and falls, it opera es through an inclined bar 68 which reacts on the control of the pilot valve 67, so that the piston of the power cylinder has a 'step-by-step movement or is compensated and may assume intermediate positions, depending upon the variations in pressure applied to the bell 56. The power cylinder 48, its pilot valve 67 and its inclined compensating bar 68 areof the type disclosed in'the-Peebles Patents Nos.

Patents Nos. 1,338,924 and 1,371,243 to which reference may be made for the details of construction.

The operationof my flue gas analyzing apparatus in controlling combustion may be briefly. summarized as follows:

If the carbon dioxide content of the flue gas increases to above the percentage for which the device is set, the intermediate pressure in the chamber 4 increases and the pressure in the bell 56 likewise increases. This tends to displace the fluid from-the bell 56 and raises the bell, tilting the balance lever 60 in a clockwise direction as .viewedin Figures 1 and 2. The balance lever 60 operates through the rod 66 and pilot valve 67 to actuate the power cylinder 48. The piston rod will then movedownward to a predetermined amount before its downward movement is checked or compensated for by the inclined bar 68. The downward movement of the p ston rod 47 will draw out'the bight of the chain 39 by means of the pulley-46,and will adjust the stack damper 33 to a wider open position.

This will reduce the pressure in the combus-cy,

tion chamber 21, which in turn will react through the regulator 41 toincrease the opening of the damper 29 in the air duct 27 and will supply more) air through the furnace.

This will reduce and restore the carbon dioxide content of the flue gas to the desired per centage. On the other hand, if the carbon dioxide content of the gas falls below the desired percentage, the intermediate pressure in the chamber 4 will fall, the pressure at the bell 56 will be decreased, and the lever 60 will be moved in a counterclockwise direction trol the power cylinder 48 which will raise as viewed in Fimlres 1 and 2. The lever 60,

will operate through the pilot valve 67 to con- Leeeeev the piston rod 47 and through the chain 39 adjust the stack damper 33 to reduce the stack draft and consequently reduce the air for combustion drawn through the furnace. This will restore the proper proportions of;

13, as shown in Figure 7. The gas is then,

delivered to the inlet pipe 3 in which it is maintained at a constant pressure by means of the constant pressure device 17a which, like the constant pressure device 17, consists of a tube 18a which discharges excess gas beneath I the surface of a liquid bath 19a. 1,339,000 and 1,492,604 and the Hopwood The chamber 4 is connected y the pipe 54a to a pressure gauge 5a and a ell 56a. The

bell 56a is carried on a balance beam 60a.

The other end of thebalance beam is provided with a bell 57a, the interior of which is'open to the atmosphere through a throttle opening controlled by a valve 69. As explained above, the pressure in the chamber 4 will always be superatmospheric. This pressure is applied to the bell 56a is balanced by a weight 65a. The weight 65a is adjusted so thatthe beam 60a will assume a horizontal or balanced position for a pressure in the chamber 4 and bell" 56a corresponding to the desired carbon dioxide percentage of the flue gas. If the carbon dioxide percentage increase, the pressure in the chamber 4 and bell 56a increases, and the lever 6011 will be tilted in a clockwise direction, as viewed in Figure 3, and will operate through the rod 66 and pilot valve 67 to actuate the power cylinder 48 and draw down the piston rod 47 and its pulley 46 and through the chain 39 open the stack damper 33 and increase the ratio of air to fuel and restore thei'carbon dioxide content to the desired amount. If the carbon dioxide content decreases, the reverse operations will take place.

While it is preferred to first pass the fluid to be analyzed through a capillary or lamellar restriction and then through an orifice or turbulent flow restriction, as shown in Fi ures 2 and 3, the restrictions may be reverse and the gas may be first passed through'an orifice or turbulent flow restriction 2b, and then through a capillary or lamellar flow restriction 1?), as illustrated in Figure 6. Therefore, when in my claims I speak of passing the fluid through lamellar and turbulent flow restrictions in series, or through turbulent and lamellar flow restrictions in series, I do not intend to limit, the passage of the fluid order, unless so explicitly specified.

While it is preferred, in a device such as shown in Figure 2, in which a differential pressure is secured by balancing the intermediate pressure of the gas to be analyzed throu h such restrictions in any particular against the intermediate pressure of the air,

provided. For example in Figure 4, the gas to be analyzed is passed through a capillary tube 10 and an orifice 20, and the intermediate pressure in the chamber 40 is balanced against an intermediate pressure in the chamber 90 into which the air is admitted through an orifice 60 and from which it is discharged throu h another orifice 70.

In igure 5 there is illustrated another modification in which the air pressure the chamber 9d and which is balanced against the chamber 4d, is secured by passing the air through two capillary tubes 6d and 703.

For purposes .of simplicity and diagram-. matic illustration,'the lamellar flow restrictions are illustrated in Figures 2 to 6, inclusive, as being capillary tubes. In actual practice, such tubes present certain objections, such as difficulty of calibration'adjustments and liability of stoppage by a single particle of solid matter. In actual practice, I prefer to use for the lamellar or capillary flow restriction a plug of porous material. Such a device is illustrated in Figure 8. It consists of a plug of porous material; This may be any suitable material, but I have found a satisfactory material to be porous earthenware; I have used for this purpose a plug made of a filter block material. These filter blocks are made and sold under various trade names, the material known as Filtros being a well known material. Filtros consists of crushed silica grains bonded so as to be porous. It may be obtained in various degrees of porosity. A plug of this character presents a large number of fineopen ings so that if one opening becomes clogged with a particle of dust, the flow is not appreciably lessened The flow through a porous plug is of the .lamellar type provided the POI'GSz are fine be used in my apparatus, but the lamellarflow only is usefully effective. The turbulent flow efiect simply reduces the effectiveness of the component of the pressure drop across the porous plug which is due to the lamellar flow. Therefore, I do not intend that the expression lamellar flow restriction as used herein shall be limited to a flow restriction having purely lamellar flow characteristics, but include a flow restriction which has lamellar flow characteristics although it may have in addition turbulent flow characteristics. Also a restriction which operates primarily upon turbulent flow may have some lamellar flow characteristics and therefore the expression turbulent flow restriction is intended to include such a restriction. The terms lamellar and turbulent flow restrictions, as used herein, are intended as relative terms and todefine two restrictions, the flow in the first being more nearly lamellar than in the second and the flow in the second being more nearly turbulent than in the first. While it is preferred to have the flow through the lamellar and turbulent fiow restrictions substantially all lamellar and turbulent, respectively, the desired effect may be'produced by the relative lamellar and turbulent flow characteristics of two restrictions in which the fiow may not be purely lamellar and turbulent.

The porous plug maybe arranged as shown in Figuer 8 so that-its resistance to flow may be adjusted, As shOWn in Figure 8, the plug is held in a sleeve 71 in which it may be adjusted so that more or less of the plug is included within the sleeve. If the plug is adjusted to the right, as shown in Figure 8, its resistance to flow may be decreased.

' Another form of capillary flow restriction which may be adjusted is shown in Figure 9. Thisconsists of a screw block 72, which is held in a threaded sleeve 73, there being a clearance left at the bottom of the threads, as indicated at 74., By turning the screw plug 7 2 in and outof the sleeve, the length of the capillary opening 74; at the bottom, of the threads may be varied and consequently its resi'stance to flow.

" 'While I have specifically illustrated and "and practiced in methods of and apparatus for regulating combustion, within the scope of the appended claims.

I claim:

1. The method of regulating combustion of fuel in a furnace, which comprises continuously passing a sample of the combustion with the carbon dioxide content of the combustion gas, and regulating the relative sup plies of fuel and air in accordance with such pressure variations. 1

2. The method of regulating combustion of fuel in a furnace, which comprises passing a sample of the combustion gas through turbulent and lamellar flow restrictions in series,

. and regulating the combustion in accordance with the pressure intermediate such. restric tions.

3. The method of regulating combustion of fuel in a furnace, which comprises passing a sample of the combustion gas through turbulent and lemellar flow restrictions inseries, and regulating the combustion in accordance with the pressure drop across one of the restrictions.

4. The method of regulating combustion of fuel in a boiler furnace, comprising primarily regulating the supply of fuel and air to the furnace by and in accordance with the load on the boiler, passing a sample of the combustion gas through lamellar and turbulent flow restrictions'in series so that the pressure intermediate the restrictions varies in accordance with the carbon dioxide content of the combustion gas, and modifying p the primary regulation by and in accordance with such pressure variations.

5. The method of regulating combustion of fuel in a furnace, comprising passing a sample of the combustion gas through lamellar and turbulent flow restrictions in series,

passing a gas of fixed composition through similar lamellar and turbulent fiow restrictions in series at the same initial and final pressures as those of the combustion gas flowing through the first set of flow restrictions, and regulating combustion in accord ance with the differential pressure variations between points intermediate the fi-ow.restrictions of each set of flow restrictions caused by variations in the carbon dioxide content of the combustion gas.

6. The method of regulating combustion of fuel in a furnace, comprising passing a sample of the combustion gas through turbulent and lamellar flow restrictions in series, passing a gas of fixed compositionthrough a second set of flow restrictions in series so that the differential pressure between points intermediate the flow restrictions of each set of flow restrictions varies in accordance with the carbon dioxide content of the combustion gas, and controlling the proportions of fuel and air supplied to the furnace by and in accordance with such pressure variations.

7. Apparatus for regulating combustion of fuel in a furnace, comprising two similar sets of lamellar and turbulent flow restrictions connected in series, means for passing combustion gas through one set of flow restricassess? tions and air through the other set of flow restrictions at the same initial and final pressures, and means for controlling proportions of the fuel and air supplied to the furnace in accordancewith the differential pressure variations between points intermediate the flow restrictions of each set.

8. Apparatus for regulating combustion of fuel in a furnace, comprising lamellar and turbulent flow restrictions connected in series, means for passing combustion gas through said restrictions so that the pressure intermediate the restrictions varies in accordance with the composition of flue gas, and means for controlling the proportions of fuel and air supplied to the furnace .in accordance with such pressure variations.

9. Apparatus for regulating the combustion of fuel in a furnace, comprising two dea sample of the combustion gas from the furnace through said devices, and means for controlling the proportions of fuel and air suplied to the furnace in accordance with the differential effects upon said devices due to variations in the density and viscosity of the combustion gas.

10. Apparatus for regulating combustion of fuel in a boiler furnace, comprising means for primarily controlling the air and fuel supplies to the furnace by and in accordance with the demand on the boiler, means for Withdrawing combustion gas and passing it through lamellar and turbulent flow restrictions in series with a substantially constant pressure drop over the two restrictions, and means for ,secondarily regulating the fuel and air proportions by and in accordance with the pressure variations developed at a point intermediate said flow restrictions by variations in the composition of the combustion gas.

11. Apparatus for regulating combustion of fuel in a boiler furnace, comprisingmeans for primarily regulating the supplies of fuel \and air to the furnace by and in accordance with the demand on the boiler, means for withdrawing combustion gas and passing it through lamellar and turbulent flow restrictions in-series, means for passing a gas of fixed composition through a similar set of lamellar and turbulent flow restrictions at restrictions by variations in the compositio of the combustion gas. I

12. The method of regulating combustion of fuel in a boiler furnace, comprising primarily regulating the supply of fuel and air to the furnace by and in accordance with the load on the boiler, passing a sample of the combustion gas through such a flow restriction that the rate of flow varies with the vis cosity of the combustion gas, and modifying the primary regulation by and in accordance.

with the variations in pressure drop over the restriction caused by variations in the cordance with pressure variations caused by the variations in the carbon dioxide of the combustion gas passing through the restriction.

14. The method of regulating combustion of fuel in a furnace, which comprises bringing a sample of the combustion gas to a predetermined temperature, passing the same through a flow restriction, and regulating the combustion by and inaccordance with the variations in pressure drop over the restriction caused by variations in the carbon dioxide content of the combustion gas passing through such restriction.

15. The method of regulating combustion of fuel in a furnace, which comprises bringing a sample of the combustion gas to a predetermined temperature and humidity, passing the same through a flow restriction, and

v regulating the combustion by and in accordance with the variations in pressure drop over the restriction caused by variations in the carbon dioxide content of the combustion gas passing through such restriction.

16. The method of regulating combustion of fuel in a furnace, comprising passing a sample of the combustion gas through a flow restriction, passing a gas of fixed composition through a similar flow restriction at substantially the same temperature as that of the sample of the combustion gas, and regulating the combustion by and in accordance with the differential variations in pressure drop over the restrictions caused by variations in the carbon dioxide content of the combustion gas passing through such restriction.

17. The method of regulating combustion of fuel in a furnace, comprising passing a sample of the combustion gas through a flow restriction, passing a gas of fixed composition through a simliar flow restriction at substantially the same temperature and humidity as that of the sample of the combustion as, and regulating the combustion by and 'm accordance with the differential variations in pressure drop over the restrictions caused by variations in the carbon dloxide content of the combustion gas passing through such restriction. 7

18. Apparatus for regulating combustion of fuel in a furnace, comprising a turbulent flow restriction, a pump for passing a sample of the combustion gas from the furnace through said turbulent flow restriction, dispensing means functionally interposed between the pump and the restriction, said dispensing means operating substantially independently of changes in density of the combustion gas, and means for controlling the proportions of fuel and air supplied to the furnace by and in accordance with the pressure variations caused by variations in the carbon dioxide content of the combustion gas passing through the flow restriction.

19. Apparatus for regulating combustion of fuel in a furnace, comprising a conduit for passing a sample of the combustion gas from the furnace, means for producing a difference in pressure to cause fluid fiow .through the conduit, dispensing means separate from drop over said turbulent flow restriction caused by variations in the carbon dioxide content of the combustion gas passing through such restriction.

20. Apparatus for regulating combustion of fuel in a boiler furnace, comprising means for primarily controlling the air and fuel supplies to the furnace by and in accordance with the demand on the boiler, means inclu ing a dispensing device for withdrawing combustion gas and passing it through a. flow restriction,'said dispensing device being of such a character that it dispenses the combustion gas at a rate which varies with the viscosity of the combustion gas, and means for secondarily regulating the fuel and air proportions by and in accordance with the variations in pressure drop over said restriction caused by variations in the carbon dioxide content of the combustion gas passing through such restriction.

'21. Apparatus for regulating combustion of fuel in a boiler furnace, comprising means for primarily controlling the air and fuel lent flow restriction, said dispensing device operating substantially independently of changes in density of the combustion gas, and

' means for secondarily regulating the fuel and air proportions by and in accordance with the variations 1n pressure drop over said restriction caused by variations in the carbon dioxide content of the combustion gas passing through such restriction.

In testimony whereof I have hereunto set my hand.

GEORGE W. SMITH. 

